Signature of Tc above 111 K in Li-doped (Bi, Pb) -2223 superconductors: synergistic nature of hole concentration, coherence length and Josephson interlayer coupling

Understanding the bottleneck to drive higher critical transition temperature Tc plays a pivotal role in the underlying study of superconductors. We systematically investigate the effect of Li^+ substitution for Cu^2+ cations on the Tc, hole concentration, coherence length and interlayer coupling, and microstructure in Li-doped Bi₁. ₆Pb₀. ₄Sr₂Ca₂Cu₃O₁₀ + or (Bi, Pb) -2223 compound. Remarkably, we demonstrate by utilizing a long-time sintering accompanied by a multiple recurrent intermediate stages of calcining and pressing within our renovated solid-state reaction method, the optimal Li-doped (Bi, Pb) -2223 samples achieve the well-enhanced Tc of 111--113. 8 K compared with the standard value of 110 K. We evince the superconducting mechanism that the substitution of Li^+ for Cu^2+ ions on the CuO₂ layers causes augmenting the hole concentrations and promotes the correlation between the overdoped outer and the underdoped inner CuO₂ planes, and thus effects improve Tc. Following a universal quadratic relation between Tc and hole concentration, a new higher optimal hole concentration is provided. Additionally, by analyzing the Aslamazov-Larkin and Lawrence-Doniach theories on the reliable excess conductivity data near the critical temperature, we observe the strong effect of Li-doping on the system. The coherence length steadily increases versus the Li-doped content, while the Josephson interlayer coupling strength between the CuO₂ layers almost remains a constant for the whole series of Li-doping. Our findings establish an insightful roadmap to improve the critical temperature and intrinsic superconducting properties in the Bi-2223 compounds through the doping process.